Feeding Value of Silages

Ensiling is an effective method of preserving feed with a minimum of nutrient loss. If ensiled properly the nutritive value is similar to that of the standing forage crop. Since fewer field losses occur when forage is ensiled than when it is put up as hay, material for ensiling often contains more nutrients than hay. However, there is a slight loss in quality during the ensiling process because plant sugars are degraded and proteins are broken down. The ultimate comparison between hay and silage will thus be influenced by the weathering and leaf losses which occurred during the haying process and the type of fermentation which existed during the ensiling process. In general, however, when rains are expected during the forage harvesting period, more nutrients are conserved with silage than with hay.

Chemically, fresh forage and silage differ greatly in two ways. Firstly, silage contains less water-soluble carbohydrates than fresh forage since these are utilized in the production of organic acids in the ensiling process. These organic acids do not have a large effect on the nutritional value of the material since they are produced in the rumen of the animal in varying amounts in any case. Secondly, considerable amounts of forage protein are degraded to non-protein nitrogen compounds such as amino acids, amines and ammonia in the ensiling process. Protein degradation products in silage are not as nutritionally useful as intact proteins in most feeding circumstances, and amines in particular may cause adverse reactions and a lower feed intake in animals.

Generally, the digestible energy content of silage is quite similar to that of the forage from which it was made. Although the crude protein of silage is similar to the original forage, 10 per cent or more of the protein in the forage will have been degraded to non-protein nitrogen. The mineral content of silages is as high as in the original forage unless measurable amounts of seepage have occurred. Silage made from green forage at the proper stage of maturity and without excessive heating in the silo can be a good source of vitamin A for animals. Since sunlight is necessary for the formation of vitamin D in forages after cutting, silage which has been left in the field for only a short period of time will contain little vitamin D.

If growing or lactating animals are fed forage-based diets, the amount of forage which the animals will voluntarily consume is very important since this will determine the ultimate nutrient intake of the animal.

Once animals become accustomed to the taste of silage, they find it quite palatable, but for the first few days of the feeding period consumption can be quite low. Even when accustomed to silage, animals will generally eat less dry matter when silage is fed than when the same forage is fed in the fresh form. Also, ruminants will normally consume more dry matter when fed good hay than they will when fed silage of the same quality. With sheep the voluntary consumption of forage is decreased more through ensiling than with cattle.

Animals will eat more dry matter from drier silages than they will from wetter silages. The reasons for this are not completely clear, but it is known that the extra water in the silage is not the explanation. Decreased intake of high moisture silage has been related to the various amines and ammo nia produced when protein is degraded and to the formation of other organic compounds. Also, more total acids are produced with wetter silage and it has been shown tha voluntary intakes can be increased if the acids in these silage are neutralized at the time of feeding.

Voluntary consumption of haylage and silage is increase by reducing the length of chop in the forage.

How much silage should be fed

Since silage usually contains more than 50 per cent water animals have to consume more silage than hay to meet their nutrient requirements. In calculating amounts of silage to be feed, the moisture content of the silage must be known so that the dry matter content of the material can be calculated. The dry matter content of silage will be essentially the same as the dry matter content of the forages put into the silo unless excessive seepage has occurred.

The following table shows the hay equivalents of silages with differing moisture contents. This can be used to estimate the amount of silage that should be fed.

It is also possible to calculate the amount of silage required by using the following procedures:
1. Calculate the dry matter content of silage as:
% DM = 100 - 40 % moisture
2. Calculate amount of silage to feed as:
kg dry matter required x 100 divided by % dry matter in silage.

Example: If 11kg of hay (91% dry matter) daily will meet the requirements of a cow for the winter, it can be calculated that they will get 10 kg dry matter from the hay (11 x 91 divided by 100). If silage contained 60% moisture then it contains 40% matter (100-60). The amount of silage which must be fed can be calculated as 10 x I00 divided by 40 = 25 kg daily.

Calves less than four months of age
Diet should not contain large amounts of silage. It tends to cause scouring and calves will not eat enough of it to meet their nutrient requirements. Some silage will not hurt them. As long as the animals are receiving enough milk, grain, protein, mineral and vitamin supplements to meet most of their nutritional requirements, silage can be fed as the only roughage source.

Growing calves from five months to ten months of age
Silage can be fed as the major constituent of the ration. There will, however, be a need for grain and other supplements to provide the animals with enough nutrients to gain at the minimum rate required for optimal productivity and economy. It is well to remember, though, that animals will normally eat less dry matter as silage than they will as hay, therefore, the amount of grain in the diet may have to be increased slightly when silage is fed. This is of particular importance when high moisture silage is fed.

Fattening cattle
Silage is a very good feedstuff to include in feedlot diets since it tends to reduce the incidence of bloat. For the first couple of days in the feedlot, hay is the preferred form of forage for cattle. Some of the animals may not be used to silage. Resulting low feed intakes can contribute to an increased incidence of sickness and poor performance at this time.

Replacement heifers over a year of age
These can be fed a silage based diet without grain supplementation provided the silage is of good quality.

Mature beef cows
Silage can be fed as the only source of energy and protein in winter. Only in extreme cases will protein supplementation be required. In all-forage diets, however, trace mineralized salt supplementation should be provided and phosphorus supplementation may be required. Vitamin D supplementation of silage diets is required in the winter. Vitamin A supplementation is recommended even though carotene levels may be high in the silage.

When good quality silage is available it may be advisable to limit the amount of silage fed daily and allow the cows to fill up on straw. This will result in a less costly ration and will prevent the cows from getting too fat. In cold weather, and as the time of calving gets closer, the amount of silage fed can be increased, and if necessary grain can be added to the diet.

Beef cows with calves
Silage made from high quality forage which contains less than 70 per cent moisture will usually be adequate without supplemental grain for beef cows nursing calves. If the silage contains more than 70 per cent moisture, or if it is of only average to poor quality, or if the level of milk production in the cows is high, supplemental grain or good quality hay will be required. If silage is being considered as the main feedstuff for nursing cows, it will be useful to have the forage tested since protein and other nutrient deficiencies are quite possible.

Breeding bulls
Feeding silage does not affect the quantity or quality of semen produced by bulls. Therefore silage can form the complete ration for bulls if mineral and vitamin supplementation are available. Supplemental protein will often be required when grass silages are fed. If the condition of a bull is poor, or the silage contains more than 70 per cent moisture, or the silage is of poor quality, supplemental good quality hay or grain should be considered.

Milking dairy cows
Silage is a good feed for milking cows if attention is paid to harvesting the forage at the proper stage of maturity.

Silage has been used successfully as the only forage source in the diet of milking cows. Diets based on silage as the only forage may contribute to low butterfat test. This appears to be caused by the short chop length common in silage which results in a reduction in the "effective fibre" content of the ration. In situations where this is a problem, various corrective measures can be taken including the addition of long or coarsely chopped hay in the ration. Increasing the length of cut may also be beneficial in higher moisture silages.

Problems can occur with off-flavored milk when cows are fed silage just prior to milking, especially grass silage that contains high levels of butyric acid. The off-fiavor can appear if cows breathe the odor. Where this situation occurs, feeding the offending silage after milking may reduce or eliminate the problem.

Sheep
Some time is required for sheep to get used to the taste of silage, thus it should be introduced gradually into a diet over a two week period.

Silage can be fed to young growing lambs but grain, protein, mineral and vitamin supplements will be required to achieve acceptable growth rates.

Silage can provide the only roughage source for mature sheep once they get used to its taste. Some ewes, however, will not eat enough silage to meet their nutritional requirements. This is particularly true for ewes carrying twin lambs since rumen capacity is reduced because space in the abdominal cavity is taken up by the developing lambs. Silage of low nutrient content or excessively wet silage may not be consumed in sufficient quantity to meet nutrient requirements. Such silage should be supplemented with grain or good quality hay.

Horses
Silage is not usually thought of as a feed for horses but it can be fed as the only roughage source in the diet of mature horses. Care should be taken to make sure that the silage has not become moldy while in the silo or after it has been removed from the silo. Moldy feed should not be fed to horses at any time.

Ketosis
There can be an increased incidence of ketosis in dairy cows fed silage as compared to cows fed hay. This problem is more likely to occur when poorly fermented silage with high levels of butyric acid is fed since butyric acid is metabolized to ketone bodies in the animal. There also may be problems with reduced intakes, which can cause ketosis, if lactating cows are switched from a hay to a silage diet too rapidly. Extra care should, therefore, be taken when lactating cows are switched to a silage-based diet, especially when they are not accustomed to silage.

Ketosis has also been reported to be a predisposing factor to pregnancy toxemia in pregnant ewes.

Nitrate poisoning
Nitrate-nitrite poisoning has been reported in animals fed silage. The amount of nitrate present in silage is always less than that which was present in the original crop. From 30 to 70 per cent or more of the nitrate in the original forage is degraded in the ensiling process. This, however, does not guarantee that nitrate toxicity will not occur when a high nitrate containing forage is conserved as silage. It appears that little degradation of nitrates occurs when the pH of the silage drops below 5. There is more degradation of nitrates in silage which has undergone an undesirable type of fermentation than in silage in which a desirable type of fermentation has taken place. Where nitrate poisoning could be a problem, it is advisable to test for nitrates. Most feed testing laboratories do nitrate tests quickly and inexpensively.

Nitrogen dioxide poisoning
Silo gas has claimed many lives. Always assume nitrogen dioxide, which is poisonous, is present in tower silos. When nitrates are degraded in the ensiling process, nitrogen oxides are formed as products of microbial metabolism. The nitrogen dioxide which results when nitrogen monoxide contacts air is often called 'silo gas' and is highly toxic to humans and animals when present in concentations greater than 10 to 25 ppm. Pulomonary edema occurs when the gas combines with water in the lining of the resipratory tract and this can cause pneumonia-like symptoms and death. Even if the gas does not casue death, respiratory tract damage can occur. Relapses are common after apparent recovery.

Since nitrogen dioxide is heavier than air, the brown gas is sometimes clearly visble inside silos or around silo openings. Most of the nitrogen dioxide is evolved from the silage in the first week of fermentation, with production peaking at two or three days after ensiling. There is essentially no nitrogen dioxide production after the material has been in the silo for more than 10 days.

In one survey, 42 per cent of all silos tested contained nitrogen dioxide high enough to be considered hazardous to human health.

Listeriosis
Listeriosis is a disease caused by the bacteria Listeria monocytogenes. The disease is commonly associated with silage but it can occur when silage is not being fed. It is also known as circling disease. Affected animals crowd into a corner, lean against fences and move in circles when walking. The disease affects the nervous system. Incoordination, high temperatures, lack of appetite, blindness, salivation and paralysis of jaw muscles also occur. The disease is usually fatal, especially with sheep, and those animals which survive have brain damage. Usually no more than 8-10 per cent of cattle are affected. The organism can also cause abortion in the third trimester of pregnancy.

Bacteria causing listeriosis are present on the vegetation and grow in the ensiling process only if the pH of the silage is above 4.2. The disease is more common in cold weather and when the animal undergoes stress. Nutrient deficiencies also may trigger the disease.

Listeria monocytogenes organisms also infect man so that precautions should be observed when handling an aborted fetus or in tasting silage to estimate quality.

Moldy silage is caused by fungi which grow readily on wet material when it is exposed to air. Under certain circumstances these organisms may produce mycotoxins which have adverse effects on animals. Moldy silage can cause severe diarrhea, loss of appetite, abortion, muscular tremors, pneumonia, changes in the lung, allergic reactions and death. Mycotoxins can also affect the microorganisms in the rumen.

However, in most instances small amounts of molds will not cause problems when fed to livestock.

Botulism
The microorganism Clostridium botulinum can grow in silage under conditions which favor clostridial organisms. Symptoms of this disease include paralysis of the throat, profuse salivation, lack of muscular coordination and often death. Cattle are less susceptible to botulism than horses since the toxin responsible for the problem is rapidly inactivated by ruminal microbes.

Dicoumarol poisoning
Sweet-clover contains varying amounts of coumarin. This chemical is often converted to dicoumarol in moldy feeds. Dicoumarol interferes with the blood clotting mechanism in animals and can result in excessive bleeding, anemia and death when fed to livestock. If sweet-clover silage is being made, care should be taken to avoid mold formation by carefully covering and sealing the silo. Also when feeding silage discard any moldy portions of the silage. It is often advisable to limit the amount of sweetclover in the diet, particularly before the calving or lambing period. Low coumarin varieties of both yellow and white sweet-clover are now available but older varieties are high in coumarins.